The VIPER structure has to deliver a successful experiment in about 80km height. It needs to sustain the electronic systems and sensitive measurement instruments and withstand slightly less than 20g’s of launch acceleration and about 20g’s in all axis while falling back to the earth’s surface. The experiment has to be built around the center of the rocket – to guarantee a stable flight trajectory – and should not endanger the health of the rocket or the success of the other experiments. Outside air pressure will be about 0,05 mbar and the ambient temperature will fall below -70°C.

Requirements

The main requirements from the science team and the REXUS manual for our experiment, in order to reach our scientific goal safely, are as follows:

The heat probes need to be deployed in µ-g and pushed against the ice surface. A depth of minimum 40mm is required to be molten into the ice-cylinder. For the end of the experiment and the safety of the rocket, it is required to retract the heatprobes back into their initial, fixed state.

The experiment needs to be absolutely sealed off from the rest of the rocket. Experiment byproducts (here: water vapor and air) should be forced out through venting holes on the outer side of the rocket.

The cooled ice samples should be inserted about 50 minutes before launch. For that, it is required to construct a removable ice sample container (ISCA) and a late access hatch.

The ice samples shall not warm up to more than -30°C prior to the measurement.

2. ISCA (Ice Sample Container Assembly)

The ISCA is the part of the experiment that needs to be integrated as late as possible, as the ice is being exposed to the ambient conditions since then. After the insertion by late access procedure, which basically means that this part will be inserted through the hatch, the rocket has to pass some checks for about 50 to 90 minutes. In the worst case (e.g. abortion of the countdown), the ISCA needs to be replaced. To allow a holding time as long as possible before having to abort the launch, the ISCA is filled with dry ice snow just minutes prior to insertion.

Distilled water will be frozen to ice and cooled to -70°C. Each of the three ice containers has 9 temperature sensors (three for each layer). Those temperature sensors are covered in thermally conductive epoxy to protect the sensors. Due to fluid-tightness concerns, the ISCA uses a PCB-feedthrough on the bottom to transmit signals from the inside to the outside of the containment. Epoxy is used to permanently seal the gap between Shell and PCB-feedthrough. An O-Ring is used to ensure a leak-free seal between ISCA and Cupola, against which the part is pushed against with the lifting mechanism.

3. Lifting Mechanism

Sectional View of the Lifting mechanism

In order to seal off the ice samples from the rest of the rocket to protect the other experiments and own equipment, a mechanism pushes the ISCA against the Cupola. This will be done by a worm gear and spindle drive combination during the Late Access Procedure. The self-locking property of the worm gear allows for a strong lock between those two components.

Lifting the ISCA with the mechanism will be done by hand, using a torque wrench attached to a flex shaft.

4. Cupola

The Cupola is the cap of the ISCA. It is fixed inside the rocket module and contains HPPM Assembly, cameras and a venting system for the developing steam/water particles during the experiment. The venting system will also normalize the pressure to the ambient level (<5mbar).

A camera is placed centrally on the ceiling of the Cupola and looks downward through a hole. With that one we can observe the melting process on all three ice samples.

5. HPPM (Heat Probe Pushing Mechanism)

Sectional view of one HPPM – 3 of them form the HPPM Assembly.

The HPPM is the moving device of the experiment, it consists out of one guide, spring and heat probe per ice container. The springs will push down the heat probes towards the ice. For the purpose of this event not happening until the experiment and after, an electric motor with a spindle drive will retract the heat probes or keep them retracted with the help of a rope drive. Optical sensors are attached to the bottom of every heat probe and will measure the travel length and speed.

HPPM Assembly with captions.

The Assembly holds all three HPPMs and guides their cables to the motor by using a pulley system. The whole HPPM Assembly will be assembled beforehand and then put inside the Cupola.

The spindle drive uses steel cables to pull the heat probes and is able to move those upwards or release them. The springs inside each HPPM push the heat probes downwards while tensioning springs are used to keep the steel cables stiff, so – even though they are properly guided and held in place – the cables don’t drop off the pulleys.

Each HPPM has one optical encoder on an own cantilever, which is used as a reference to get the melting distance from.